Why IVF isn't one thing
A common source of confusion — and sometimes anxiety — is when someone's IVF experience looks very different from another person's. Different medications, different timelines, different numbers of injections. What one person describes as IVF can sound almost unrecognisable to someone who went through a different protocol.
This isn't inconsistency. It reflects the fact that IVF is a framework — a set of steps that can be configured in different ways depending on the individual. The core sequence (stimulation, egg collection, fertilisation, transfer) remains constant. What changes is how each step is approached, and with what intensity.
Your protocol isn't better or worse than someone else's. It's the one calibrated for your body, your history, and your diagnosis.
The main types of IVF
Standard IVF uses hormone injections to stimulate the ovaries to develop multiple follicles simultaneously. The aim is to retrieve several eggs in a single collection, increasing the chances that at least one will fertilise and develop into a transferable embryo. Once collected, eggs and sperm are placed together in a dish and fertilisation happens naturally in the laboratory.
This is the protocol most people go through, and the one that most IVF statistics are based on. The stimulation phase typically lasts 8–14 days, with regular monitoring scans and blood tests to track follicle development and adjust medication doses.
Most suited to: people with unexplained infertility, tubal factor, or moderate ovarian reserve where sperm quality is not a significant concern.
ICSI follows an identical path to standard IVF through stimulation and egg collection. The difference is what happens in the embryology laboratory: rather than placing eggs and sperm together and allowing fertilisation to occur naturally, a single sperm is selected by an embryologist and injected directly into each mature egg.
ICSI was developed to address male factor infertility, and it remains the standard approach when sperm count, motility, or morphology is compromised. It's also used when previous standard IVF cycles have had unexpectedly poor fertilisation rates, or when sperm has been surgically retrieved. Many clinics now offer ICSI routinely across all cycles; others reserve it for specific indications.
Most suited to: male factor infertility, low fertilisation in previous cycles, surgically retrieved sperm, or where the embryologist recommends it based on egg or sperm quality at collection.
Natural cycle IVF collects the single egg that the body produces naturally each month, without any stimulation injections. Monitoring scans track the naturally developing follicle, and when the egg is ready, collection is timed using the body's LH surge or a small trigger injection. Fertilisation and transfer then proceed as in standard IVF.
The appeal is its simplicity — no daily injections, no hormonal side effects, lower cost per cycle, and no risk of ovarian hyperstimulation syndrome (OHSS). The limitation is that only one egg is collected per cycle, so the chances of having a transferable embryo from any given cycle are lower than with stimulated IVF. It may suit those who respond poorly to stimulation, those who prefer minimal intervention, or those for whom stimulation carries specific risks.
Most suited to: poor responders to stimulation, those who prefer low-intervention treatment, those with medical reasons to avoid stimulation hormones, or those who have philosophical objections to the creation of multiple embryos.
Mild IVF (sometimes called mini IVF) uses lower doses of stimulation medication than standard IVF, typically aiming to collect 2–7 eggs rather than the larger numbers sought in conventional cycles. The medication burden is reduced — both in terms of daily dose and duration — and the cost of drugs per cycle is lower.
The rationale is that quality matters more than quantity: retrieving fewer, better-quality eggs may yield equally good or better embryos than retrieving many from an over-stimulated ovary. Evidence on this remains debated, and outcomes depend heavily on individual circumstances. Mild IVF is not the same as natural cycle IVF — stimulation still occurs, just more gently.
Most suited to: people with a good ovarian reserve who prefer fewer drugs, poor responders who don't tolerate high stimulation well, or those for whom a lower-intervention approach is medically or personally preferable.
A frozen embryo transfer cycle uses an embryo that was frozen during a previous IVF cycle rather than creating new embryos. The stimulation and egg collection phases are skipped entirely. Instead, the focus is on preparing the uterine lining — either in a natural cycle, with light medication support, or in a fully medicated cycle — so the embryo has the best possible environment for implantation. In a medicated FET, a short course of down-regulation medication is often used first to suppress the natural cycle, giving the clinic precise control over the timing of the lining preparation and transfer.
FET cycles are significantly less demanding than full IVF cycles, and their success rates have improved markedly with modern vitrification. For many people with frozen embryos, a FET is the next step after an unsuccessful fresh transfer, or the planned route when a freeze-all strategy was used from the outset. In some situations — particularly where OHSS risk is elevated — freezing all embryos and transferring in a subsequent cycle is recommended as standard practice.
Most suited to: anyone with frozen embryos from a previous cycle; those where a fresh transfer wasn't possible or advisable; planned freeze-all cycles (common in PCOS).
Donor egg IVF uses eggs provided by another person — either a known donor or an anonymous donor through a clinic's programme. The recipient does not undergo stimulation or egg collection; instead, the uterine lining is prepared to receive the embryo, which is created from the donor's eggs and sperm (from a partner or donor). The transfer process is then the same as any FET or fresh transfer cycle.
Donor egg IVF has the highest success rates of any IVF type, because donor eggs are typically from people with established fertility and good egg quality. It's recommended where egg quality or quantity is significantly reduced, where previous IVF cycles have repeatedly produced no viable embryos, or for those without ovaries. In the UK, donors must be identifiable — children born from donor conception have the right to access donor information at 18.
Most suited to: significantly reduced ovarian reserve, repeated IVF failure with own eggs, premature ovarian insufficiency, or those who have been advised that the chances of success with their own eggs are very low.
Stimulation protocols — long vs short
Within standard IVF, the way stimulation is managed varies by protocol. This is another source of confusion — two people both doing "standard IVF" may be on very different medication schedules. The most common distinction is between the long (agonist) and short (antagonist) protocols.
| Protocol | How it works | Duration | Typically used when |
|---|---|---|---|
| Short protocol GnRH antagonist |
Stimulation starts at the beginning of the cycle. A GnRH antagonist is added from around day 5–6 to prevent premature ovulation | ~11–14 days of injections | Now the most common protocol. Suits most patients, lower OHSS risk, quicker overall timeline |
| Long protocol GnRH agonist (downregulation) |
The natural cycle is first suppressed using a GnRH agonist for 2–4 weeks, then stimulation begins. Gives the clinic more control over timing | 4–6 weeks total | Certain endometriosis cases, some poor responders, or where the clinic needs precise cycle control |
| Freeze-all Stimulation + collection, no fresh transfer |
All suitable embryos are frozen after collection. Transfer happens in a separate FET cycle, once the body has recovered from stimulation | Stimulation cycle + separate FET | High OHSS risk (common in PCOS), elevated progesterone at trigger, or when embryo testing (PGT-A) is planned |
Your clinic will recommend a protocol based on your AMH, antral follicle count, previous cycle responses, and diagnosis. It's entirely reasonable to ask your consultant why a particular protocol has been chosen for you — and what the alternatives would be. A good clinic will welcome that conversation.
IVF and PCOS — a specific consideration
PCOS (polycystic ovary syndrome) is one of the most common conditions affecting fertility, and it requires particular care in an IVF context. People with PCOS typically have a high antral follicle count — meaning the ovaries contain many small follicles ready to respond to stimulation. This is in some ways an advantage, but it also creates a significant risk: the ovaries can over-respond to stimulation, causing ovarian hyperstimulation syndrome (OHSS).
OHSS ranges from mild discomfort to a serious medical complication in its most severe form. For people with PCOS, careful stimulation management is essential — using lower starting doses, monitoring response closely, and being prepared to adapt the protocol.
The freeze-all approach is now standard practice for many PCOS patients: all suitable embryos are frozen after collection, and transfer happens in a subsequent medicated FET cycle once the ovaries have settled. This significantly reduces OHSS risk while preserving the embryos for transfer. A GnRH agonist trigger — rather than the conventional hCG trigger — is also commonly used in PCOS cycles, again to reduce OHSS risk.
The good news is that people with PCOS who do respond to IVF often produce good numbers of eggs and embryos. The challenge is managing the response safely — which experienced clinics handle routinely. If you have PCOS, ask your clinic specifically about their approach to OHSS prevention and whether a freeze-all strategy is planned from the outset.